Funds are requested to purchase a ConfoCor 2 Fluorescence Correlation Microscope combination system from Carl Zeiss, Inc. This state-of-the-art instrument combines a laser scanning confocal microscope (LSM) with a special purpose detection head, electronics, and software for Fluorescence Correlation Spectroscopy (FCS) measurements. The ConfoCor 2 is especially well suited for FCS measurements on cells for which the LSM provides an excellent means of locating the measurement volume relative to cell structures. The software and automated control of filters, apertures, and specimen location facilitate rapid and flexible measurements on biological systems. Studies now in progress and in planning that will employ the ConfoCor 2 include the following: 1. Conformational fluctuations of proteins in the native state; 2. Restricted diffusion of matrix metalloprotease enzyme molecules on oriented collagen fibers; 3. Interactions of actin capping protein and Arp2/3 complex with actin filaments in cells; 4. Conformational fluctuations of flexible macromolecules such as DNA and unfolded polypeptides; 5. Binding constants of the signal transduction intermediates MEK and ERK in living cells. Projects 1 and 4 address fundamental problems in molecular biophysics. Projects 2, 3, and 5 address important issues relating to cell-tissue interactions, cell motility, and essential cellular regulatory mechanism. Each project has significant potential for contributions to health-related research.